This invention relates to a smoke detector and alarm which is capable of detecting white and gray smoke as well as black smoke and which is self-monitoring and entirely reliable regardless of fluctuations in line voltage.
A fire in a residential or a commercial building generates heat and smoke. Heat detector alarms have been used with a certain degree of success, but often times a fire is well established before sufficient heat is given off to trigger such a device. Because smoke build-up is much more rapid than heat, especially in confined areas having insufficient oxygen to support combustion, attempt have been made to provide an earlier alarm by detecting the first presence of smoke and quickly sounding an alarm. Devices proposed for this purpose are usually designed to detect small particles suspended in air, i.e., smoke, which generally rise from the source of the fire. Typical smoke detector devices are described in U.S. Pat. No. 2,537,028 issued Jan. 9, 1951 to Kahusac et al., U.S. Pat. No. 3,382,762 issued May 14, 1968 to Vasel et al., U.S. Pat. No. 3,383,670 issued May 14, 1969 to Roberts and U.S. Pat. No. 3,497,303 issued Feb. 24, 1970 to Enemark et al.
However, prior art smoke detector devices are complex and costly in structure, often requiring expensive lenses and other special parts such as a porous housing. Moveover, prior devices have proven to be not entirely reliable or capable of meeting UL (Underwriters' Laboratory, Inc.) standard for smoke detectors. These standards require flawless operation at elevated temperatures, self-monitoring capabilities and, most importantly, reliability at all times, regardless of line voltage variations which can, undesirably, cause premature triggering of the alarm directly or indirectly by creating a temporary imbalance in the otherwise sensitive smoke sensing systems. Prior art smoke detectors have failed to fully meet all of these requirements and at the same time provide an economic smoke detector unit for wide and diverse use.
The present invention provides such a smoke detector and alarm which is capable of detecting white and gray smoke as well as black smoke and which is self-monitoring and entirely reliable regardless of line voltage variations.